Introduction to Permutations and Combinations. Quantitative Literacy

1. Permutations
and
Combinations

2. Objectives:
 apply fundamental counting principle
 compute permutations
 compute combinations
 distinguish permutations vs combinations

3. Fundamental Counting
Principle
Fundamental Counting Principle can be used
determine the number of possible outcomes
when there are two or more characteristics .
Fundamental Counting Principle states that
if an event has m possible outcomes and
another independent event has n possible
outcomes, then there are m* n possible
outcomes for the two events together.

4. Fundamental Counting
Principle
Lets start with a simple example.
A student is to roll a die and flip a coin.
How many possible outcomes will there be?
1H 2H 3H 4H 5H 6H
1T 2T 3T 4T 5T 6T
12 outcomes
6*2 = 12 outcomes

5. Fundamental Counting
Principle
For a college interview, Robert has to choose
what to wear from the following: 4 slacks, 3
shirts, 2 shoes and 5 ties. How many possible
outfits does he have to choose from?
4*3*2*5 = 120 outfits

6. Permutations
A Permutation is an arrangement
of items in a particular order.
Notice, ORDER MATTERS!
To find the number of Permutations of
n items, we can use the Fundamental
Counting Principle or factorial notation.

7. Permutations
The number of ways to arrange
the letters ABC: ____ ____ ____
Number of choices for first blank? 3 ____ ____
3 2 ___
Number of choices for second blank?
Number of choices for third blank? 3 2 1
3*2*1 = 6 3! = 3*2*1 = 6
ABC ACB BAC BCA CAB CBA

8. Permutations
To find the number of Permutations of
n items chosen r at a time, you can use
the formula
.
0
where n
r
r
n
n
r
p
n 



)!
(
!
60
3
*
4
*
5
)!
3
5
(
!
5
3
5 




2!
5!
p

9. Permutations
A combination lock will open when the
right choice of three numbers (from 1
to 30, inclusive) is selected. How many
different lock combinations are possible
assuming no number is repeated?
Practice:
Answer Now

10. Permutations
A combination lock will open when the
right choice of three numbers (from 1
to 30, inclusive) is selected. How many
different lock combinations are possible
assuming no number is repeated?
Practice:
24360
28
*
29
*
30
)!
3
30
(
!
30
3
30 




27!
30!
p

11. Permutations
From a club of 24 members, a
President, Vice President, Secretary,
Treasurer and Historian are to be
elected. In how many ways can the
offices be filled?
Practice:
Answer Now

12. Permutations
From a club of 24 members, a
President, Vice President, Secretary,
Treasurer and Historian are to be
elected. In how many ways can the
offices be filled?
Practice:
480
,
100
,
5
20
*
21
*
22
*
23
*
24
)!
5
24
(
!
24
5
24





19!
24!
p

13. Combinations
A Combination is an arrangement
of items in which order does not
matter.
ORDER DOES NOT MATTER!
Since the order does not matter in
combinations, there are fewer combinations
than permutations. The combinations are a
"subset" of the permutations.

14. Combinations
To find the number of Combinations of
n items chosen r at a time, you can use
the formula
.
0
where n
r
r
n
r
n
r
C
n




)!
(
!
!

15. Combinations
To find the number of Combinations of
n items chosen r at a time, you can use
the formula
.
0
where n
r
r
n
r
n
r
C
n




)!
(
!
!
10
2
20
1
*
2
4
*
5
1
*
2
*
1
*
2
*
3
1
*
2
*
3
*
4
*
5
)!
3
5
(
!
3
!
5
3
5







3!2!
5!
C

16. Combinations
To play a particular card game, each
player is dealt five cards from a
standard deck of 52 cards. How
many different hands are possible?
Practice:
Answer Now

17. Combinations
To play a particular card game, each
player is dealt five cards from a
standard deck of 52 cards. How
many different hands are possible?
Practice:
960
,
598
,
2
1
*
2
*
3
*
4
*
5
48
*
49
*
50
*
51
*
52
)!
5
52
(
!
5
!
52
5
52





5!47!
52!
C

18. Combinations
A student must answer 3 out of 5
essay questions on a test. In how
many different ways can the
student select the questions?
Practice:
Answer Now

19. Combinations
A student must answer 3 out of 5
essay questions on a test. In how
many different ways can the
student select the questions?
Practice:
10
1
*
2
4
*
5
)!
3
5
(
!
3
!
5
3
5 




3!2!
5!
C

20. Combinations
A basketball team consists of two
centers, five forwards, and four
guards. In how many ways can the
coach select a starting line up of
one center, two forwards, and two
guards?
Practice:
Answer Now

21. Combinations
A basketball team consists of two centers, five forwards,
and four guards. In how many ways can the coach select a
starting line up of one center, two forwards, and two
guards?
Practice:
2
!
1
!
1
!
2
1
2 

C
Center:
10
1
*
2
4
*
5
!
3
!
2
!
5
2
5 


C
Forwards:
6
1
*
2
3
*
4
!
2
!
2
!
4
2
4 


C
Guards:
Thus, the number of ways to select the
starting line up is 2*10*6 = 120.
2
2
5
1
2 * C
C
C 4
*